Electrostatic printing device and electrode unit used in the electrostatic printing device

ABSTRACT

An electrode unit capable of printing images with an excellent quality and a printing device provided with this electrode unit. Rows of apertures (L 1 , L 2 ) formed by disposing apertures ( 11 ) in s preset direction of a base material consisting of a resin film or a resin sheet are provided, non-image forming sections ( 15, 15 ) not used for forming images are defined along a length at least 50 times, preferably at least 200 times, the thickness of the base material extending from the opposite ends of the base material in the rows of apertures (L 1 , L 2 ) lengthwise direction, and an image forming section ( 16 ) is formed in the remaining portion. Apertures ( 11 ) and control electrodes ( 12 ) surrounding the apertures ( 11 ) are used to control the transfer of toner particles to form images.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an electrostatic printing device forforming an image using toner particles in printers, facsimiles, copyingmachines and so on, and parts therefor.

2. Description of the Prior Art

Printing devices, by which electric signals output from computers, wordprocessors, facsimiles, or the like are formed as visible images on arecording medium such as paper or the like, include an electrostaticprinting device 1 shown in FIG. 5, in which an electrode unit isarranged between a particle carrier and a back electrode.

The electrostatic printing device 1 generates an electric potentialdifference between the particle carrier 20 and the back electrode 30 tocreate an electric field, by which toner particles are conveyed towardthe back electrode 30 from the particle carrier 20, and the electrodeunit 10 arranged between the particle carrier 20 and the back electrode30 controls conveyance of toner toward the back electrode 30 from theparticle carrier 20 to enable forming of a desired image on a recordingmedium 50, such as paper or the like, or an intermediate recordingmedium, such as a transfer belt or the like, disposed between theparticle carrier 20 and the back electrode 30.

The above-mentioned electrode unit 10 comprises apertures 11 and controlelectrodes 12 surrounding the apertures 11 at least partially (see FIG.6), and voltage applied on the control electrodes 12 has an influence onan electric field, by which toner particles are conveyed toward the backelectrode 30, so that toner particles conveyed toward the back electrode30 from the particle carrier 20 determine positions, sizes and the likeof dots formed on the recording medium 50.

The electrode unit 10 is formed from a base material of a resin film orresin sheet composed of, for example, a resin material such as polyimideor the like and having a thickness of around 25 to 200 μm, the basematerial being formed with a plurality of apertures 11 aligned in apredetermined direction, and the apertures 11 being formed to be atleast partially surrounded by, for example, mutually intersectingcontrol electrodes or the control electrodes 12 formed in a ring-shapedfashion.

When being assembled into the printing device 1, the electrode unit 10is disposed between the particle carrier 20 and the back electrode 30such that rows of the apertures (L1 to L4) of the unit 10 are made inparallel to an axis of the particle carrier 20, which is formed as acolumn or cylinder-shaped rotating body.

In the example shown in FIG. 5, the electrode unit 10 is formed withfour rows of apertures (L1 to L4) disposed in parallel. In the casewhere the plural rows of apertures (L1 to L4) are provided in theelectrode unit 10, a distance between the surface of the particlecarrier 20 and the apertures 11 formed on the electrode unit 10 variesdepending upon, for example, to which of the rows of apertures (L1 toL4) the apertures 11 belong, when the electrode unit 10 is positioned ina planar manner.

In the specification of the present application, assuming that Lkdenotes a distance between the respective apertures 11 of the electrodeunit 10 and the surface of the particle carrier 20, Lk is large betweenthe apertures 11 belonging to the right and left rows (L1, L4) in FIG. 5and the surface of the particle carrier 20 and small between theapertures 11 belonging to the central rows (L2, L3) and the surface ofthe particle carrier 20. Also, since even with an electrode unit 10comprising one or two rows of apertures, it is difficult to arrange therow or rows of apertures in completely parallel to the axis of theparticle carrier, Lk is in some cases varied in the apertures 11belonging to the same row. Therefore, as Lk is varied, the controlelectrodes 12 have different influences on an electric field formedbetween the particle carrier 20 and the back electrode 30 even in thecase where the same voltage is applied to the control electrodes 12surrounding the apertures 11 in the respective rows (L1 to L4) ofapertures, so that dots formed on the recording medium 50, such as paperor the like, vary in size and density depending upon which of thecontrol electrodes 12 surrounding the apertures 11 has controlled theforming of the dots.

By way of example, in the case where dots are formed on the recordingmedium 50 assuming that all the control electrodes 12 surrounding theapertures 11 (L1 to L4) formed on the electrode unit 10 in the printingdevice 1 shown in FIG. 5 are the same in electric potential, when theapertures 11 belonging to the rows L2, L3 and having a relatively smalldistance Lk between them and the surface of the particle carrier 20 formrelatively deep and large dots, and the apertures 11 belonging to therows L1, L4 and having a relatively small distance Lk between them andthe surface of the particle carrier 20 form light and small dots,quantity of toner particles adhered to a printed surface finished andsizes of dots formed differ depending upon, through which of theapertures 11 adherence of toner particles and formation of dots aremade, when dots are consecutively shown in, for example, FIG. 6, so thatthere are produced areas being uneven in density and not printed, suchunevenness and non-printed areas being visually recognized as lines.

Such phenomenon is called “white line noise”, which causes degradationin printing quality, and removal of which is contemplated. In order toprevent generation of such “white line noise”, distances Lk between thesurface of the particle carrier 20 and the apertures 11 formed on theelectrode unit 10 are made constant to eliminate variation ΔLk in thedistances, thereby solving the problem of “white line noise”. Therefore,there has been proposed a printing device (see FIG. 7) constructed suchthat distances Lk between the apertures 11 of the electrode unit 10 andthe surface of the particle carrier 20 are made uniform in all the rows(L1 to L4) by bending that area of the electrode unit 10, in which theapertures 11 are formed, so that all the apertures 11 are adjusted to bedisposed on a circle concentric with an outer periphery of the particlecarrier 20.

As described above, with the printing device 1, in which the area of theelectrode unit 10 formed with the apertures 11 is bent in compliancewith the surface configuration of the particle carrier 20, all thedistances Lk between the surface of the particle carrier 20 and therespective rows (L1 to L4) of the apertures of the electrode unit 10 areuniform, and therefore it is possible to prevent that degradation inprinting quality, which is attributed to unevenness in such distances.

When the electrode unit 10 formed from a base material of a resin filmor resin sheet is bent in a certain direction, the cross section of thebent portion itself undergoes deformation in its inner surface with theresult that such deformation causes the electrode unit 10 to change inshape.

For example, when an X—X axis of an electrode unit 10 put in a state ofbeing disposed in a planar position shown in FIG. 8 is bent into a shapeshown by a broken line X′—X′ as shown in FIG. 9, the electrode unit 10generates warp ρ at both ends in the direction along a Z—Z axisperpendicular to the X—X axis thus bent (see FIG. 9).

FIG. 10 shows a state of a minute space containing an origin O and cutfrom the bent portion of the electrode unit 10 put in the state shown inFIG. 9. When the electrode unit 10 is bent in a widthwise direction in asquare column above the origin O (above the broken line) in FIG. 10,normal stress acts to compress the electrode unit 10 in the directionalong the X—X axis, thereby generating longitudinal strain ε_(x) andlateral strain ε_(x)(=−νε_(x)) in the direction along the Z—Z axis sincethe electrode unit 10 compressed by the normal stress tends to expand ina lateral direction.

Also, stress and strain in a state opposite to the above are generatedin a square column below the origin O (below the broken line) in FIG.10. Therefore, when the electrode unit 10 is bent in the direction alongthe X—X axis, stress is generated in the direction along the Z—Z axis totend to bend the electrode unit 10. This stress is liable to be releasedat ends of the substrate, so that “warp” which affects the print qualityis caused in both end portions of the substrate in the direction alongthe Z—Z axis (see FIG. 11).

Thus, when the electrode unit 10 is bent in the direction perpendicularto the rows of apertures, “warp” is produced in both longitudinal endportions of the rows of apertures, so that degradation in printingquality is caused in the case where apertures 11 are formed up to endportions of the electrode unit 10 and all the apertures 11 are used forformation of an image. That is, the apertures 11 formed in both endportions of the electrode unit 10 are displaced in directions away fromthe surface of the particle carrier 20 to make distances Lk large togenerate dispersion between the apertures 11 in the same rows.Therefore, in the case where such displacement is generated to a degreehaving an influence on printing quality, that is, beyond an error in anallowable range, dots formed are different in size and density betweenthe respective apertures 11 to cause degradation in printing quality.

However, there have not been conventionally proposed any method anddevice for dissolving that degradation in image quality, which is causedby “warp” generated in both longitudinal end portions of an electrodeunit 10.

Accordingly, the present invention has been made with a view toovercoming the above disadvantages of the prior art and has its objectto provide an electrode unit capable of forming an image of excellentquality by eliminating variations in distances between apertures formedon an electrode unit and the surface of a particle carrier as far aspossible even if “warp” is generated at both end portions of rows ofapertures in a longitudinal direction of rows of apertures when theelectrode unit is bent in the direction perpendicular to the rows ofapertures.

SUMMARY OF THE INVENTION

In order to attain the above object, an electrostatic printing device 1and an electrode unit 10 used for the electrostatic printing device 1according to the present invention are provided, the electrostaticprinting device comprising a column-shaped or cylinder-shaped particlecarrier 20 carrying toner particles on the surface thereof, a backelectrode 30 disposed opposite the particle carrier 20 and an electrodeunit 10 arranged between the particle carrier 20 and the back electrode30 and formed with a plurality of apertures 11, which are at leastpartially surrounded by control electrodes 12, and wherein electricvoltage producing an electric potential difference between the particlecarrier 20 and the back electrode 30 and applied to the controlelectrodes 12 of the electrode unit 10 controls conveyance of tonerparticles toward the back electrode 30 from the particle carrier 20 toform a desired image on a recording medium 50 disposed between theparticle carrier 20 and the back electrode 30, and the electrode unit 10comprises a substrate formed from a resin film or resin sheet, theapertures 11 being arranged in a predetermined direction of thesubstrate to provide rows of apertures (L1, L2), the rows of apertures(L1, L2) on the electrode unit 10 being arranged in the directionparallel to an axis of the particle carrier 20, the electrode unit 10being arranged to be curved in the direction perpendicular to thelongitudinal direction of the rows of apertures (L1, L2), and therespective rows of apertures (L1, L2) being positioned equidistantlyfrom an outer periphery of the particle carrier 20, and wherein when thesubstrate is bent in the direction perpendicular to the rows ofapertures (L1, L2), the substrate curves in the longitudinal directionof the rows of apertures (L1, L2) to create an image forming area 16defined by that portion on the substrate, in which displacements(variations ΔLk) produced in directions away from the surface of theparticle carrier 20 are in a predetermined range of allowable error, andimage unforming areas 15, 15 being not used for formation of an imageand defined by those areas, which extend from both ends of the imageforming area to both ends of the substrate.

In addition, the image unforming areas 15, 15 may comprise areas, inwhich the apertures 11 are not formed, and the apertures 11 may beformed. However, the apertures 11 formed in the image unforming areas15, 15 are not used for formation of an image.

The image unforming areas 15, 15, respectively, are provided to extendover a length fifty times or more, more preferably, two hundred times ormore a thickness of the substrate in the longitudinal direction of therows of apertures.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become understood fromthe following detailed description of preferred embodiments thereof inconnection with the accompanying drawings in which like numeralsdesignate like elements, and in which;

FIG. 1 is a plan view showing an electrode unit according to the presentinvention;

FIG. 2 is a schematic view illustrating a printing device according tothe present invention;

FIG. 3 is an explanatory view showing holding means, to which theelectrode unit is mounted;

FIG. 4 is an explanatory view showing an example, in which the electrodeunit is mounted to the holding means;

FIG. 5 is a schematic view illustrating a conventional printing device;

FIG. 6 is a view illustrating the generation of white line noise;

FIG. 7 is a schematic view illustrating a conventional printing devicewith an electrode unit curved;

FIG. 8 is a view illustrating an electrode unit;

FIG. 9 is a view illustrating an electrode unit in a curved state;

FIG. 10 is a view illustrating how strain is generated in an electrodeunit in a curved state; and

FIG. 11 is a view illustrating “warp” in a longitudinal direction of theelectrode unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below withreference to the accompanying drawings.

In FIG. 1, the reference numeral 10 denotes an electrode unit accordingto the present invention. The electrode unit 10 is called a flexibleprinted board (FPC) and is formed from a base material of a resin filmor resin sheet composed of, for example, a resin material such aspolyimide or the like and having a thickness of around 25 to 200 μm, andformed with a multiplicity of apertures 11 extending through the basematerial, the apertures 11 being formed to be at least partiallysurrounded by a control electrodes 12. In the present embodiment, themany apertures 11 having a diameter of around 160 μm are formed in thebase material having a diameter of 100 μm to form the electrode unit 10.

The control electrodes 12 are shown as comprising ring-shaped portions12 a surrounding the respective apertures 11 and lead portions 12 b forconnecting the ring-shaped portions 12 a of the respective controlelectrodes 12 to an electric voltage source (not shown) in theembodiment shown in FIG. 1. The control electrodes 12 is not limited toa configuration shown in FIG. 1 but may be one, in which a plurality ofintersecting control electrodes surround the apertures at leastpartially, and one, in which control electrodes are provided to surrounda plurality of apertures 11 at a time, and can use various knownconfigurations.

Also, the control electrodes 12 may be formed on either of front andback surfaces of the above base material composed of a resin film orresin sheet, or may be formed on both surfaces of the base material, orfurther may be embedded in and disposed on the base material, and is notlimited to arrangement, configuration and the like provided thatconveyance of toner particles toward the back electrode 30 can becontrolled.

In the embodiment shown in FIG. 1, the apertures 11 are arranged in thedirection along the line Z—Z to define rows (L1, L2) of apertures, and aplurality of rows (L1, L2) of apertures are arranged in parallel in thedirection along the line X—X, so that two rows. (L1, L2) of aperturesare formed in the embodiment shown in FIG. 1.

It should be noted that these rows (L1, L2) of apertures are not limitedto two-row arrangement but may be arranged in two or more rows and canalso be applied to one row arrangement.

With the electrode unit 10 constituted in the above manner, an image isformed through the apertures 11 formed in an image forming area 16, andimage unforming areas 15, 15 being not used for formation of an imageare formed on both ends of the image forming area 16.

The image forming area 16 used for formation of an image comprises thatportion on the substrate, in which displacements (variations ΔLk)produced in directions away from the surface of the particle carrier 20are in a predetermined range of allowable error when the substrate ofthe electrode unit curves in a longitudinal direction (direction alongthe line Z—Z in FIG. 1) of the rows (L1, L2) of apertures after thesubstrate is bent in the direction (direction along the line X—X inFIG. 1) perpendicular to the rows (L1, L2) of apertures, and theapertures 11 formed in the image forming area 16 and the controlelectrodes 12 surrounding the apertures 11 control conveyance of tonerparticles to control positions, sizes and densities of dots formed.Also, the image unforming areas 15, 15 being not used for formation ofan image are formed on those areas of the substrate, which extend fromboth ends of the image forming area 16 to both ends of the substrate.

In what extent the image unforming areas 15, 15 should be provided, thatis, what extent from both ends of the electrode unit 10 correspond tothose portions, in which large variations ΔLk are generated, isdetermined by a thickness of the substrate of the electrode unit 10 suchthat large variations ΔLk are generated in portions at a distance fiftytimes or less the thickness of the substrate, more surely a distance twohundred times or less the thickness of the substrate, from both ends ofthe electrode unit 10. Therefore, those portions define the imageunforming areas 15, 15 and the remaining portion defines the imageforming area 16, in which the apertures 11 and the control electrodes 12surrounding the apertures 11 control conveyance of toner particles toform an image, thereby enabling prevention of degradation in printingquality.

In the present embodiment, the resin substrate of the electrode unit 10has a thickness of about 100 μm, so that the image unforming areas 15,15 are provided over lengths of 5 mm, more surely 2 cm or more from bothends of the electrode unit 10 whereby degradation in printing qualitycan be prevented even if “warp” of the substrate occurs at bothlongitudinal ends thereof.

In addition, while the apertures 11 are also formed in the imageunforming areas 15, 15 in the present embodiment shown in FIG. 1, theapertures 11 may not be formed in the image non-forming areas 15, 15. Inthe case where the apertures 11 are formed in the image unforming areas15, 15, the apertures 11 formed in the image unforming areas 15, 15should not be used for formation of an image by not connecting to thecontrol electrodes 12 surrounding those apertures to a voltage source(not shown). Thus, in the case where the apertures 11 are formed notonly in the image forming area 16 but also in the image unforming areas15, 15, there is no need of any complex work for forming (or notforming) the apertures 11 partially in manufacture of the electrode unit10, so that the electrode unit 10 can be manufactured easily.

In this manner, the image unforming areas 15, 15 being not used forformation of an image are provided over a distance fifty times or lessthe thickness of the substrate of the electrode unit 10, more surely adistance two hundred times or less the thickness of the substrate inboth ends of the electrode unit 10 in the longitudinal direction of therows of apertures, whereby it is possible to prevent that dispersion indistances Lk between the apertures 11 and the surface of the particlecarrier 20, which is caused by “warp” produced at both longitudinal endsof the rows of apertures when the electrode unit 10 is bent in thedirection perpendicular to the rows of apertures as described later.

The electrode unit 10 constituted in the above manner is arrangedbetween the particle carrier 20 and the back electrode 30 to form aprinting device 1 shown in FIG. 2 while that area, in which theapertures 11 are formed, is bent in compliance with a circle concentricwith the outer peripheral shape of the particle carrier 20.

In FIG. 2, the electrostatic printing device 1 comprises the particlecarrier 20 formed in a cylindrical-shape, the back electrode 30, and theelectrode unit 10 arranged between the particle carrier 20 and the backelectrode 30.

In the electrostatic printing device 1, the particle carrier 20 is inthe form of a column-shaped or cylinder-shaped rotating body, andconstructed such that upon rotation of the particle carrier 20, tonerparticles T filled in a container 60 adhere to the surface of theparticle carrier 20 to be conveyed thereby.

In the case where, for example, toner of magnetic substance is used astoner particles, the particle carrier 20 may be formed in the form of acylinder, in which magnets are arranged, and may be constructed to beable to electrically adhere toner particles to the surface thereof, andcan adopt various known configurations.

In this manner, upon rotation of the particle carrier 20, tonerparticles having adhered to the surface of the particle carrier 20 areconveyed to a position, in which the apertures 11 of the electrode unit10 are formed, and toner particles can be conveyed toward the backelectrode 30 by an electric field formed by electric potentialdifference given between the particle carrier 20 and the back electrode30.

In the electrostatic printing device 1, the electrode unit 10 arrangedbetween the particle carrier 20 and the back electrode 30 is constructedto be held in a curved state so that distances Lk between the apertures11 in the rows (L1, L2) of apertures formed on the electrode unit 10 andthe surface of the particle carrier 20 are made uniform.

In order to hold the electrode unit 10 in a curved state, the printingdevice 1 in the present embodiment comprises holding means 40 for theelectrode unit 10. An example of the holding means 40 is shown in FIG.3, and the holding means 40 for holding the electrode unit 10 of thepresent invention in a curved state is not limited to a configurationshown in FIG. 3.

In FIG. 3, the holding means 40 comprises a frame formed to besubstantially rectangular-shaped, and the electrode unit 10 formed to berectangular-shaped is arranged in the frame. A side of the electrodeunit 10 is, for example, interposed between holding portions 41 providedon a side of the holding means 40 to be fixed at its one end, and a sidefacing the above side is made a free end which is not fixed to theholding means 40.

Further, the holding means 40 comprises pressing means 42 provided on aside thereof opposite to the side, on which the holding portions 41 areformed, and for pushing a free end side of the electrode unit 10 upwardand bending the same in FIG. 3, the pressing means 42 in the presentembodiment comprising a push pin inserted into a hole 43 formed in aside of the frame of the holding means 40 to be able to advance orretract and extending through the frame in FIG. 3.

When a side of the electrode unit 10 is interposed between the holdingportions 41 of the holding means 40 constructed in the above manner andthe free end side of the electrode unit 10 is pushed up by the abovepushing pin 42, the electrode unit 10 formed from a resin material suchas polyimide or the like to posses flexibility is curved as shown inFIG. 4. A position, in which the electrode unit 10 is bent, can beadjusted by advancing and retracting the pushing pin 42 such thatbending of the electrode unit 10 can be generated near and toward theholding portions 41 by moving the pushing pin 42 toward the holdingportions 41 and bending of the electrode unit 10 can be shifted awayfrom the holding portions 41 by moving the pushing pin 42 in thedirection away from the holding portions 41, such adjustment enablingbending of the electrode unit 10 to correspond to a position, in whichthe apertures 11 are formed.

The curved electrode unit 10 is arranged to conform to the outerperiphery of the particle carrier 20 in the form of a columnar orcylindrical configuration, and the respective apertures 11 are madeequidistant from the outer periphery of the particle carrier 20.

In addition, the electrode unit 10 may be arranged in such a manner thateither or both of portions disposed right and left of that area, inwhich the apertures 11 are formed, contact the surface of the particlecarrier 20 in FIG. 4, in which case a material involving less frictionalresistance may be adhered to the contact portion between the electrodeunit and the particle carrier 20.

In this manner, the electrode unit 10 arranged between the particlecarrier 20 and the back electrode 30 is constructed such that thecontrol electrodes 12 surrounding the apertures 11 are connected to avoltage source (not shown) and when a predetermined voltage is appliedto the control electrodes 12 through a control device (not shown) or thelike, conveyance of toner particles toward the back electrode 30 fromthe particle carrier 20 is controlled to form a desired image on arecording medium 50, such as paper or the like, disposed between theparticle carrier 20 and the back electrode 30.

The electrode unit constituted in the above manner and the printingdevice provided with the electrode unit are arranged in a state, inwhich the image forming area of the electrode unit is curved to be ableto be disposed on a circle concentric with the outer periphery of theparticle carrier which is formed into a columnar or cylindrical shape,so that all distances between the respective apertures formed on theelectrode unit and the surface of the particle carrier become the samewhereby unevenness in printing among the apertures in the respectiverows is eliminated, dots printed through the respective apertures are ofthe same size and the same density, and printing quality is improvedwithout generation of “white line noise” as shown in FIG. 6.

Also, when the electrode unit is bent in the direction perpendicular tothe rows of apertures, the substrate of the electrode unit curves in alongitudinal direction of the rows of apertures to create an imageforming area defined by that portion on the substrate, in whichdisplacements produced in directions away from the surface of theparticle carrier are in a predetermined range of allowable error, andimage unforming areas being not used for formation of an image anddefined by those portions, which extend from both ends of the imageforming area to both ends of the electrode unit, whereby it is possibleto provide an electrostatic printing device and an electrode unit usedfor the same, in which no conspicuous error is generated in distancesbetween the apertures and the particle carrier due to the warp generatedin the longitudinal direction of the rows of apertures of the electrodeunit caused by bending of the electrode unit, and dots formed can bemade as uniform as possible in size and density.

Thus the broadest claims that follow are not directed to a machine thatis configure in a specific way. Instead, said broadest claims areintended to protect the heart or essence of this breakthrough invention.This invention is clearly new and useful. Moreover, it was not obviousto those of ordinary skill in the art at the time it was made, in viewof the prior art when considered as a whole.

Moreover, in view of the revolutionary nature of this invention, it isclearly a pioneering invention. As such, the claims that follow areentitled to very broad interpretation so as to protect the heart of thisinvention, as a matter of law.

It will thus be seen that the objects set forth above, and those madeapparent from the foregoing description, are efficiently attained andsince certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatters contained in the foregoing description or shown in theaccompanying drawings shall be interpreted as illustrated and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:
 1. In electrostatic printing device comprising acolumn-shaped or cylinder-shaped particle carrier carrying tonerparticles on the surface thereof, a back electrode disposed opposite theparticle carrier, and an electrode unit arranged between the particlecarrier and the back electrode and formed with a plurality of apertureswhich are at least partially surrounded by control electrodes, andwherein electric voltage producing an electric potential differencebetween the particle carrier and the back electrode and applied electricvoltage to the control electrodes of the electrode unit for controllingconveyance of toner particles toward the back electrode from theparticle carrier to form a desired image on a recording medium disposedbetween the particle carrier and the back electrode, characterized inthat; the electrode unit including: a base material of a resin film orresin sheet, the apertures being arranged in a predetermined directionof the substrate to provide rows of apertures, the rows of apertures onthe electrode unit being arranged in the direction parallel to an axisof the particle carrier, and the electrode unit being arranged to becurved in the direction perpendicular to a longitudinal direction of therows of apertures, and wherein when the substrate is bent in thedirection perpendicular to the rows of apertures, the substrate curvesin the longitudinal direction of the rows of apertures to create animage forming area defined by that portion on the substrate, in whichdisplacements produced in directions away from the surface of theparticle carrier are in a predetermined range of allowable error, andimage unforming areas being not used for formation of an image anddefined by those portions, which extend from both ends of the imageforming area to both ends of the substrate.
 2. The electrostaticprinting device according to claim 1, wherein the image unforming areasform non-apertures areas, which having no apertures.
 3. Theelectrostatic printing device according to claim 1, wherein the imageunforming areas, respectively, are provided to extend over a lengthfifty times or more a thickness of the substrate in the longitudinaldirection of the rows of apertures.
 4. The electrostatic printing deviceaccording to claim 1, wherein the image unforming areas, respectively,are provided to extend over a length two hundred times or more thethickness of the substrate in the longitudinal direction of the rows ofapertures.
 5. In an electrode unit for use in an electrostatic printingdevice comprising a column-shaped or cylinder-shaped particle carriercarrying toner particles on the surface thereof, a back electrodedisposed opposite the particle carrier, and an electrode unit arrangedbetween the particle carrier and the back electrode and formed with aplurality of apertures, which are at least partially surrounded bycontrol electrodes, and wherein electric voltage producing an electricpotential difference between the particle carrier and the backelectrode, and applied to the control electrodes of the electrode unitcontrols conveyance of toner particles toward the back electrode fromthe particle carrier to form a desired image on a recording mediumdisposed between the particle carrier and the back electrode, andcharacterized in that; the electrode unit including: a base materialformed of a resin film or resin sheet, the apertures being arranged in apredetermined direction of the substrate to provide rows of apertures,and wherein that portion on the substrate, in which displacements fromoriginal positions, produced by that curvature in the longitudinaldirection of the rows of apertures, which is generated when thesubstrate is bent in the direction perpendicular to the rows ofapertures, are in a predetermined range of allowable error, serves as animage forming area, and those portions extending from both ends of theimage forming area to both ends of the substrate serve as imageunforming areas being not used for formation of an image.
 6. Theelectrode unit for use in an electrostatic printing device according toclaim 5, wherein the image unforming areas form non-apertures areas,which having no apertures.
 7. The electrode unit for use in anelectrostatic printing device, according to claim 5, wherein the imageunforming areas, respectively, are provided to extend over a lengthfifty times or more a thickness of the substrate in the longitudinaldirection of the rows of apertures.
 8. The electrode unit for use in anelectrostatic printing device, according to claim 5, wherein the imageunforming areas, respectively, are provided to extend over a length twohundred times or more the thickness of the substrate in the longitudinaldirection of the rows of apertures.